Oil dilution control

ABSTRACT

The invention has to do with a method and control mechanism for continuously maintaining a satisfactory constant level of refrigerant concentration in the lubricating oil of a refrigeration compressor. The method consists of continuously measuring the refrigerant pressure and the oil temperature, adjusting the oil temperature in relation to the measured refrigerant pressure to maintain a substantially constant refrigerant concentration in the oil. A specific form of apparatus, particularly suitable for the practice of the method, may consist of a thermal responsive system (as a bulb, tube, and bellows) continuously measuring the oil temperature and converting the measured temperature into pressure, and a second system continuously producing a pressure commensurate to vapor pressure of the refrigerant in contact with the oil, the pressure created by the first system acting in opposition to the pressure created by the second system to produce a force differential, as measured by the systems, for operation of a differential pressure switch means to contact and disconnect an oil heater to a power supply to maintain the vapor pressure of the oil solution at a level to limit the absorption of refrigerant in the oil solution.

United States Patent V Mount et al.

[54] OIL DILUTION CONTROL [721 Inventors: Gordon L. Mount, West Monroe; James W. Endress, Syracuse, both of N.Y.

[73] Assignee: Carrier Corporation, Syracuse, N.Y.

[22] Filed: Sept. 23, 1971 [211 Appl. No.: 183,127

|$2| US. Cl. ..6 2/84, 62/192, 62/472 |51| Int. Cl ..,...F25b 43/02 158] Field 0' Search ..62/84, 192, 468, 472

[56] i I References Cited UNITED STATES PATENTS Primary Examiner-William J. Wye Attorney-Harry G. Martin, Jr. et al.

[5 7] ABSTRACT The invention has to do with a method and control mechanism for continuously maintaining a satisfactory [151 3,705,499 [451 Dec. 12, 1972 constant level of refrigerant concentration in the lubricating oil of a refrigeration compressor. The method consists of continuously measuring the refrigerant pressure and the oil temperature, adjusting the oil temperature in relation to the measured refrigerant pressure to maintain a substantially constant refrigerant concentration in the oil. A specific form of apparatus, particularly suitable for the practice of the method, may consist of a thermal responsive system (as a bulb, tube, and bellows) continuously measuring the oil temperature and converting the measured temperaturevinto pressure, and a second system continuously producing a pressure commensurate to vapor pressure of the refrigerant in contact withthe oil, the pressure created by the first system acting in opposition to the pressure created by the second system to produce a force differential, as measured by the systems, for operation of a differential pressure switch means to contact and disconnect an oil heater to a power supply to maintain the vapor pressure of the oil solution at a level to limit the absorption of refrigerant in the oil solution.

9 Claims, 2 Drawing Figures 1 OIL DILUTION CONTROL BACKGROUND OF THE INVENTION The phenomenon of refrigerant absorption into the lubricating oil of a refrigeration compressor and its attendant disadvantages are well known. Certain refrigerants, such as the refrigerant known as R-12, are

infinitely soluble in mineral oils commonly used in lo Themost troublesome aspect of high oil dilution by refrigerant is when the machine is started up. While the machine is shut down, the temperature of the a refrigerant in contact with the oil rises substantially from the operating temperature thereof. As the refrigerant temperature increases, and .therefrigerant vapor pressure on the oil increases and, accordingly, the absorption of refrigerant in the oil. The ambient temperature can easily go up to 80 F during shutdown, and the oil temperature will drop to the same level. Under this condition, dilution of the oil is excessive.

Uponstartup of the machine, the pressure in the low side thereof decreases very rapidly with the result that the refrigerant in the highly diluted oil will boil violently at the inlet of the oil pump, such as to reduce the pump capacity to the low oil pressure switch cutout point and the machine cannot be started.

Various methods have been used to prevent excessive oil dilution. It is known that oil dilution is a function of oil temperature and refrigerant pressure. It is a matter of the vapor pressures of the refrigerant and oil. Upon a decrease of oil temperature, there is a decrease in oil vapor pressure. Accordingly, if for a given refrigerant pressure, there is a decrease in oil temperature, there is an increase in refrigerant absorption. One method employed to limit refrigerant absorption is to operate a heater in the oil reservoir, the heater being controlled by a thermostat set at 140 F. 'Another method is to have the heater on continuously, the heater being sized to limit oil dilution at the highest ambient temperature incurred. While these methods will function to keep the refrigerant concentration to acceptable levels at all ambient conditions,such methods are costly and inefficient in operation, particularly in that high oil temperature is maintained regardless of the refrigerant pressure. Also, oil dilution will increase 25 percent with a decrease in heater wattage caused by a decrease in voltage of percent. Also, if the oil supply runs low, the oil becomes overheated and its lubricating properties adversely affected.

SUMMARY OF THE INVENTION The preferred embodiment of apparatus for carrying out our method consists of a closed thermal system such as a bulb, connected to a tube, which in turn is connected to a bellows or diaphragm, the system containing a temperature responsive fluid medium producing a variable pressure commensurate with the temperature being sensed. The bulb of such a system is positioned in the oil reservoir. A bulb of a like second system is located in the low side of the refrigeration apparatus. The pressures created in the two sensing thermal systems act in opposition and are employed for actuation of a differential pressure operated switch serving to establish a connection between a power supply and the oil heater. The temperature responsive fluid medium in one thermal system is different than the medium in the other system. The media are selected to produce a differential pressure producing a curve under all conditions which will give a nearly constant level of refrigerant concentration.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation of a refrigeration apparatus illustrating the control mechanism embodying our invention.

FIG. 2 is a graph depicting the operating curves of two fluid media that may be used in the thermal systems.

DESCRIPTION OF THE PREFERRED EMBODIMENT The refrigeration system disclosed is of the conventional arrangement including a centrifugal compressor having a frame structure 10 in which an impeller 11 is journaled and operatively connected through a gear box 12 to a driving motor mounted in a casing 13. The discharge from the compressor is conveyed through a line 15 to a condenser 16. The liquid refrigerant is metered through a passage 17 from the condenser to an evaporator or water chiller 18. The compressor frame 10 is formed, in the base portion thereof, with an oil reservoir 19, the normal oil level being indicated by the dash line 20. A heater 21 is mounted in the oil reservoir.

Our method consists of continuously measuring the temperature of the oil in the reservoir 19 and the pressure of the refrigerant in the low pressure area of the refrigeration system. The heater 21 is powered on the basis of the measurements to maintain the temperature of the oil relative to the refrigerant pressure to establish a differential of predetermined range between the refrigerant pressure and the oil temperature. If, for example, the pressure of the refrigerant increases in respect to the oil temperature sufficiently to bring about a differential exceeding the predetermined range, the heater is operated to raise the oil temperature to a level which, at the then existing refrigerant pressure, to bring the differential within the predetermined range to prevent excessive refrigerant absorption in the oil, that is to keep the absorption of the refrigerant to a satisfactory level.

It will become apparent that various arrangements may be used to measure the temperatures or vapor pressures of the oil and operate the oil heater in response thereto. An arrangement involving a minimum of cost and maintenance is illustrated schematically in the drawing. In this arrangement, a thermal responsive system is used to continuously measure the temperature of the oil in the reservoir. This system includes a bulb 23 positioned in the oil supply in the reservoir 19. The bulb is connected to a pressure responsive device 25 by a tube 27. A like thermal responsive system is used to continuously measure the pressure of the refrigerant in the low side of the system. In this second system, a bulb 30 is located in a low pressure area of the refrigeration system, as in the evaporator 18, and is connected to a pressure responsive device 31 by a tube 33. The area above the oil level is included in the low pressure side of the system as by the conduit 34. Each thermal system contains a quantity of fluid medium for providing a variable pressure representing a force in the system according to the temperature sensed by the bulb therein.

The pressure responsive devices 25, 31 are arranged in opposition and operatively connected to a movable switch contact 39. If the oil temperature is low, as sensed by the bulb 23, in comparison to the refrigerant pressure as sensed by the bulb 30, contact 39 is moved into engagement with contact 40. This results in a circuit being completed to the heater 21 from the power supply side 41, closed switch contacts 39, 40, wire 43, heater 21, wire 45, heater 21 to the side, 45 of the power supply.

The pressure responsive devices 25, 31 and switch contacts 39, 40 represent a conventional pressure differential operated switch. As stated above, if the refrigerant pressure applied to the device 31 exceeds the pressure applied to the device 25 by a predetermined amount, contact 39 will be moved into engagement with contact 40. It will be understood, switches of this type may be adjusted, within limits, to operate within a predetermined pressure differential or range, for example, 17 psi. Therefore, the pressure on the device 31 would have to exceed the pressure on the device 25 by 17 psi, before movement of the contact 39 into engagement with contact 40. The reverse operation is of the same order.

The fluids in the thermal systems are selected so as to provide a rate of variation between the force developed in one system being different from the rate of variation in the force developed in the other system, with the result that a predetermined force differential within the two systems is substantially independent of a fixed difference between the refrigerant pressure in the low side of the system and the temperature of the oil in the reservoir. Fluids particularly satisfactory for use in the thermal systems have been found to be refrigerant R-l 2 and ethyl chloride, the ethyl chloride being used in the thermal system 23, 27, 25. With the use of these media, it will be understood that if the refrigeration system is being operated with refrigerant R-12, then the bulb may be omitted, that system including only the tube 33 and the responsive device 31.

The operation of the two thermal systems employing the refrigerant R-l2 and ethyl chloride is shown on curves on the graph in FIG. 2. The operating curve for refrigerant R-l 2 is shown at 41 and the curve for ethyl chloride is shown at 42. It will be observed that these curves show the non-linear saturation pressures for the respective fluids and that the curves diverge with increase in temperature. As shown on the graph in FIG. 2, with a temperature of 70 F, the vapor pressure of the refrigerant is 85 psia, as shown at the intersecting point 43 of line 44 with the R-l2 curve 41. With this temperature the vapor pressure of the ethyl chloride is 20 psia as shown at the intersecting point 45 of line 44 with the ethyl chloride curve 42.

With the pressure differential operated switch having an operating range of 17 pounds, this range is greatly exceeded by the difference in the vapor pressures amounting to 65 pounds. Accordingly, the contact 39 will be moved into engagement with the contact 40. The energized heater will raise the oil temperature until the difference between the vapor pressure of the refrigerant and that of the ethyl chloride is within the operating range of the switch, which is indicated by the intersecting point'47 of the line 48, establishes the oil temperature at 140. In other words, our system has operated to raise the oil temperature from 70 to 140 to establish vapor pressure differential within the 17 pound range, which establishes a satisfactory level of oil dilution.

To illustrate another example, with a temperature of 120 F, as could exist with a rooftop unit, the vapor pressure of the refrigerant is 173 psia as determined at the intersecting point between the line 51 and the R- 12 curve 41. To bring the vapor pressure of the ethyl chloride within the operating differential of the 17 pounds, the oil is heated to a temperature of 204 F as determined by the intersecting point 53 by the line 55 and the ethyl chloride curve 42. 4

It is to be noted that as the ambient temperature goes up there is need for a greater temperature differential between the refrigerant and the oil. For example, with an ambient temperature of the oil needs to be 140 F, which is a temperature difference of 70 F. However, with an ambient temperature of the oil temperature needs to be 204, the temperature difference being 84. The divergence between the curves 41, 42 automatically provides for establishing the proper temperature difference between the refrigerant and the oil,in other words, the proper difference in vapor pressure in order to effect control of refrigerant absorption into the oil to maintain a satisfactory level of oil dilution.

While the thermal systems referred to provide a particularly satisfactory and efficient means for continuously measuring the oil temperature and the refrigerant vapor pressure, it will be apparent other systems and devices may be employed for the purpose.

While a preferred embodiment of this invention has been described for purposes of illustration, it will be appreciated that this invention may be otherwise embodied within the scope of the following claims.

We claim:

1. The method of maintaining a substantially constant level of refrigerant concentration in the lubricating oil supply or the compressor of a refrigeration system, comprising the steps of continuously measuring the refrigerant vapor pressure, continuously measuring the temperature of the oil supply, and adjusting the temperature of the oil supply in relation to the measured refrigerant vapor pressure to maintain a differential, within a predetermined range, between the measured vapor pressure of the refrigerant and the measured temperature of the oil supply.

2. A refrigeration apparatus including a refrigerant compressor having a lubricating oil reservoir containing a supply of lubricating oil and a control mechanism for maintaining a substantially constant level of refrigerant concentration in the lubricating oil, said control mechanism comprising an oil heater mounted in heat exchanging relation with the oil in said reservoir, said heater being operable when energized to raise the oil temperature, sensing means continuously sensing the refrigerant vapor pressure and oil temperature, and heater energizing means for energizing said heater in response to said sensing means sensing a differential, exceeding a predetermined range, between saidrefrigerant vaporpressure and oil temperature.

3. A refrigeration apparatus including a refrigerant compressor having a lubricating oil reservoir containing a supply of lubricating oil and a control mechanism for maintaining a substantially constant level of refrigerant concentration in the lubricating oil, said control mechanism comprising an oil heater mounted in heat exchanging relation with the oil in said reservoir, a power supply for operating said heater to raise the temperature of the oil in said reservoir, means operable to continuously produce a signal indicative of the vapor pressure of the refrigerant contacting the oil in said' oil reservoir, a temperature sensing means operable to continuously produce a signal indicative of the temperature of the oil in said reservoir, and heater v control means responsive upon the sensed refrigerant pressure signal exceeding the sensed oil temperature signal by a predetermined amount to connect said heater to said power supply.

4; A refrigeration system including a refrigerant compressor having a lubricating oil reservoir and control mechanism for maintaining a substantially constant level of refrigerant concentration in the compressor lubricating oil, said control mechanism comprising a heater mounted in said oil reservoir, a power supply for operating said heater to raise the temperature of the oil in said reservoir, a first measuring means for continuously measuring the vapor pressure of the refrigerant contacting the oil in said reservoir, a second measuring means for continuously measuring the temperature of the oil in said reservoir, and heater control means responsive to a differential exceeding a predetermined range, as measured by said first and second means, to connect said heater to said power supply to maintain a substantially constant level of refrigerant concentration in said oil supply.

5. A control mechanism as set forth in claim 4 wherein said first and second measuring means consists of thermal systems operable to produce pressure signals indicative of the refrigerant vapor pressure and oil temperature respectively and said heater control means consists of a differential pressure operated switch means.

6. A control mechanism as set forth in claim 4 wherein said heater control consists of a differential pressure operated switch means, said first measuring means includes a passage means for conveying refrigerant pressure to said switch means and said second measuring means consists of a closed thermal responsive system containing a temperature responsive fluid medium for producing a force within said system commensurate with the oil temperature and applying said force to said switch means.

7. Refrigeration apparatus including a compressor having a lubricating oil reservoir containing supply of lubricating oil and control mechanism for maintaining a constant level of refrigerant concentration in the compressor lubricating oil; said control mechanism comprising a heater mounted in heat exchanging relation to the oil in said oil reservoir; a power supply for said heater; a first thermal responsive system containing a temperature responsive fluid medium for producing a variable pressure representing a force within said system; said system sensing the temperature in the low side of said refrigeration system; a second thermal responsive system containing a temperature responsive fluid medium different from said first fluid medium for producing a variable pressure representing a force within said second system; said second system sensing the temperature of the oil in said reservoir; the force created by expansion of .fluid within the first system acting in opposition to the force created by expansion of fluid within the second system, and the rate of variation between the force and temperature in said first system being different from the rate of variation between the force and temperature in said second system so that a predetermined force differential within the two systems is substantially independent of a fixed temperature difference'between the ambient temperature in said low pressure side and the oil temperature in said reservoir; and means responsive to a predetermined force differential as measured by said systems to establish connection of said heater to said power supply.

8. A control mechanism as set forth in claim 1 wherein said means responsive to said predetermined force differential consists of a pressure operated switch operable when actuated by said force differential to tially filled with ethyl chloride.

UNITED STATES PATENT OFFICE (IERTIFICATE QQF CQRRECTION Patent No 3,7 5, +99 Dated December 972 Inv n r GORDON -L. MOUNT &' JAMES w, ENDRESS It is certified that error appears in the abov-identified patent and that said Letterebetent are hereby corrected as shown below:

ABSTRACT, line 19, cancel "contact" and insert in place Column 4, line 48,. Claim; 1, cancel*"or" and insert in place thereof -;for+- Signed and sealed this 19th day of November 1974.

(SEAL) Attest:

McCOY M GIBSON JR. c, MARSHALL DANN I Attesting-Officer I Commissioner of Patents USCOMM'DC 6Q376-P69 w 0.5. GOVERNMENT PRINTING OFFICE I959 0-366-334 FoRM Po-mso (in-s9) 

1. The method of maintaining a substantially constant level of refrigerant concentration in the lubricating oil supply or the compressor of a refrigeration system, comprising the steps of continuously measuring the refrigerant vapor pressure, continuously measuring the temperature of the oil supply, and adjusting the temperature of the oil supply in relation to the measured refrigerant vapor pressure to maintain a differential, within a predetermined range, between the measured vapor pressure of the refrigerant and the measured temperature of the oil supply.
 2. A refrigeration apparatus including a refrigerant compressor having a lubricating oil reservoir containing a supply of lubricating oil and a control mechanism for maintaining a substantially constant level of refrigerant concentration in the lubricating oil, said control mechanism comprising an oil heater mounted in heat exchanging relation with the oil in said reservoir, said heater being operable when energized to raise the oil temperature, sensing means continuously sensing the refrigerant vapor pressure and oil temperature, and heater energizing means for energizing said heater in response to said sensing means sensing a differential, exceeding a predetermined range, between said refrigerant vapor pressure and oil temperature.
 3. A refrigeration apparatus including a refrigerant compressor having a lubricating oil reservoir containing a supply of lubricating oil and a control mechanism for maintaining a substantially constant level of refrigerant concentration in the lubricating oil, said control mechanism comprising an oil heater mounted in heat exchanging relation with the oil in said reservoir, a power supply for operating said heater to raise the temperature of the oil in said reservoir, means operable to continuously produce a signal indicative of the vapor pressure of the refrigerant coNtacting the oil in said oil reservoir, a temperature sensing means operable to continuously produce a signal indicative of the temperature of the oil in said reservoir, and heater control means responsive upon the sensed refrigerant pressure signal exceeding the sensed oil temperature signal by a predetermined amount to connect said heater to said power supply.
 4. A refrigeration system including a refrigerant compressor having a lubricating oil reservoir and control mechanism for maintaining a substantially constant level of refrigerant concentration in the compressor lubricating oil, said control mechanism comprising a heater mounted in said oil reservoir, a power supply for operating said heater to raise the temperature of the oil in said reservoir, a first measuring means for continuously measuring the vapor pressure of the refrigerant contacting the oil in said reservoir, a second measuring means for continuously measuring the temperature of the oil in said reservoir, and heater control means responsive to a differential exceeding a predetermined range, as measured by said first and second means, to connect said heater to said power supply to maintain a substantially constant level of refrigerant concentration in said oil supply.
 5. A control mechanism as set forth in claim 4 wherein said first and second measuring means consists of thermal systems operable to produce pressure signals indicative of the refrigerant vapor pressure and oil temperature respectively and said heater control means consists of a differential pressure operated switch means.
 6. A control mechanism as set forth in claim 4 wherein said heater control consists of a differential pressure operated switch means, said first measuring means includes a passage means for conveying refrigerant pressure to said switch means and said second measuring means consists of a closed thermal responsive system containing a temperature responsive fluid medium for producing a force within said system commensurate with the oil temperature and applying said force to said switch means.
 7. Refrigeration apparatus including a compressor having a lubricating oil reservoir containing supply of lubricating oil and control mechanism for maintaining a constant level of refrigerant concentration in the compressor lubricating oil; said control mechanism comprising a heater mounted in heat exchanging relation to the oil in said oil reservoir; a power supply for said heater; a first thermal responsive system containing a temperature responsive fluid medium for producing a variable pressure representing a force within said system; said system sensing the temperature in the low side of said refrigeration system; a second thermal responsive system containing a temperature responsive fluid medium different from said first fluid medium for producing a variable pressure representing a force within said second system; said second system sensing the temperature of the oil in said reservoir; the force created by expansion of fluid within the first system acting in opposition to the force created by expansion of fluid within the second system, and the rate of variation between the force and temperature in said first system being different from the rate of variation between the force and temperature in said second system so that a predetermined force differential within the two systems is substantially independent of a fixed temperature difference between the ambient temperature in said low pressure side and the oil temperature in said reservoir; and means responsive to a predetermined force differential as measured by said systems to establish connection of said heater to said power supply.
 8. A control mechanism as set forth in claim 1 wherein said means responsive to said predetermined force differential consists of a pressure operated switch operable when actuated by said force differential to connect said heater to said power supply.
 9. A control mechanism as set forth in claim 1 wherein said first thermal responsive system inCludes a bulb partially filled with refrigerant R-12 and said second thermal responsive system includes a bulb partially filled with ethyl chloride. 